1. Field of the Technology
The present invention relates to a toner conveying device, a toner supply device and an image forming apparatus using these, in particular relating to a toner conveying device, toner supply device for use in an image forming apparatus that performs image forming with toner and an image forming apparatus using these.
2. Description of the Prior Art
Conventionally, in image forming apparatuses such as copiers, facsimile machines and the like using toner, toner is supplied to the developing unit by means of a toner supply device including a toner cartridge and the like so as to achieve continuous operation of image output.
As a known method of supplying toner to a developing unit by means of a toner supply device, there is a configuration in which toner is supplied from a toner cartridge to the developing unit by way of a toner conveying device.
In the toner supply device in which a toner cartridge is arranged above the developing unit, the toner conveying device is constructed so that a toner conveying path extending vertically is formed to convey the toner to the developing unit located below.
Recently in the field of image forming apparatuses, there is a trend towards high-resolution configurations. With this trend, the particle size of the toner also has become finer. Generally, the finer the toner, the worse the fluidity of the toner is. As a result, the toner becomes liable to stagnate and solidify in the toner conveying path of the toner conveying device. To deal with this, various ways of measures to solve this problem with the toner conveying device have been taken.
As a prior art example, there is a proposal of an image forming apparatus having four vertically arranged developing units for different colors wherein each developing unit is supplied with toner from a toner hopper (corresponding to a toner cartridge) and is constructed so as to be movable up and down because these developing units need to oppose a photoreceptor drum when they are operated. To achieve this operation, the toner conveying path for supplying toner from the toner hopper to each developing unit is formed of a corrugated pipe (see patent document 1: Japanese Patent Application Laid-open No. Hei 4-174467).
Arranged further at the side of this corrugated pipe is a rotator which has a plurality of projections provided on its peripheral side and is driven to rotate by a motor. That is, in patent document 1, this rotator is adapted to rotate so that the projections beat the outer peripheral surface of the corrugated pipe and strike off the toner that stagnates in the inner pleats of the corrugated pipe.
As another prior art example, there is also a proposal of an image forming apparatus which has four developing units for different colors arranged horizontally in tandem, wherein each color of toner is supplied from a separate toner cartridge to the corresponding developing unit by way of first and second conveying passages, the first passage being arranged horizontally and incorporating an auger and the second passage being arranged vertically and incorporating a spring agitator. In this configuration, the spring agitator is adapted to move up and down with rotation of the auger in the first passage to thereby prevent adherence of toner to the inner wall of the second conveying passage (see patent document 2: Japanese Patent Application Laid-open 2001-296731).
Further, there is still another proposal of an image forming apparatus which, in addition to a configuration where a toner conveying path is vibrated as described above, comprises a toner (developer) conveyance control means for controlling the amount of toner conveyance so as to control the amount of toner to be supplied through the toner conveying path (see patent document 3: Japanese Patent Application Laid-open 2005-165003).
However, any of the above conventional configurations has the problem that stagnation and solidification of toner in the toner conveying path that is arranged vertically cannot be prevented properly.
Specifically, in the configuration of patent document 1, since the vertical toner conveying passage is formed of a corrugated pipe, it is not so easy or possible to prevent stagnation and solidification of toner inside the toner conveying passage in terms of structural reason of the conveying passage. Further, since this configuration is constructed so that part of the toner conveying passage is impacted or vibrated by the rotator, there is also the problem that stagnation or solidification of toner is liable to occur at the areas away from the position of the rotator.
Also, in the configuration of patent document 2, since a spring agitator is arranged inside the second conveying passage that is arranged vertically, toner becomes prone to stagnate or solidify on the surface of the spring agitator. More explicitly, the spring agitator itself is liable to cause the problem of hindering toner conveyance.
Further, in the configuration of patent document 3, since the amount of toner being supplied through the toner conveying passage is controlled, it is necessary to vary the sectional area through which toner passes, in accordance with the amount of toner to be supplied, resulting in configuration complexity. That is, there occurs the problem that the apparatus configuration becomes complex and the maintenance performance is also affected.